Snowmobiles generally are powered by two cycle engines. Two cycle engines typically require that oil be mixed with the fuel to provide lubrication to the internal moving parts of the engine. While many small two cycle engines, such as those employed on lawn mowers, chain saws, whip string trimmers, etc., require the oil to be mixed with the fuel before the fuel is poured into the gas tank, snowmobiles typically employ a two-cycle engine oil tank connected to a fuel/oil mixing apparatus. Thus, the user can fill up the gas tank with regular gas, fill up the oil tank with two-cycle engine oil, and rely on the fuel/oil mixing apparatus to properly blend the oil with the gas just prior to delivery of the gas to the engine for combustion. While this arrangement is convenient for the user, it does require the mounting of an oil tank in a location easily accessible by the user.
The engines on some snowmobiles are simply air cooled. Higher performance and larger sized engines, however, often are liquid cooled--i.e., the engine has a water jacket connected to a radiator or other similar system for dissipating heat that is absorbed by coolant in the water jacket. The coolant may be of any suitable type, such as that commonly used in automobile engines (i.e., usually it is not just water, as water would freeze, but rather a mixture of water with, e.g., ethylene glycol). As in automobiles, desirably a coolant reservoir/overflow tank is provided to assure that the cooling system on the engine (i.e., the water jacket, radiator, etc.) is always full of coolant. This, however, also requires the mounting of a coolant reservoir in a location easily accessible by the user.
Snowmobiles typically also include an air box through which all air provided to the engine for combustion must pass. The air box may include an air filter to prevent debris from entering the engine, and it also serves to reduce engine noise by muffling somewhat the sounds generated by combustion in the engine cylinders.